This is a competitive renewal application focused on the role of the mGluR5-PKC5 signaling pathway in ethanol self-administration and reinstatement of ethanol-seeking behavior. During the current funding period, we have demonstrated that this signaling pathway is an important mediator of voluntary ethanol intake in rodents. mGluR5 receptors are biochemically coupled to PKC5 activity, and antagonists of mGluR5 receptors reduce ethanol consumption in wildtype mice but not mice lacking PKC5. We have developed a model of intravenous (i.v.) ethanol self-administration in the rat that is amenable to pharmacological manipulation of ethanol reinforcement as well as the study of reinstatement of ethanol seeking behavior, a widely used model of relapse. Using this model, we have identified the nucleus accumbens (NAc) as a critical brain region that is involved in the regulation of ethanol self-administration by signaling between mGluR5 and PKC5. Finally, we have generated novel preliminary data showing that PKC5 mediates phosphorylation of the mGluR5 receptor, which we hypothesize plays a role in regulating the ligand binding properties and surface expression of this receptor. In this renewal application, we will further examine the reciprocal signaling between mGluR5 and PKC5 as well as the neural circuitry where this signaling pathway regulates ethanol self-administration and reinstatement of ethanol-seeking behavior. In Specific Aim 1, we will examine the regulation of mGluR5 receptor function by PKC5. Specifically, we will examine changes in the ligand binding properties and cell surface expression of mGluR5 receptors in the dorsal and ventral striatum following intracerebroventricular administration of the PKC5 translocation inhibitor myr-5V1-2. In Specific Aim 2, we will examine the neural circuitry where mGluR5-PKC5 signaling mediates ethanol reinforcement. This will be examined by measuring i.v. ethanol self-administration following microinjection of the selective mGluR5 antagonist MTEP alone and in combination with the PKC5 translocation inhibitor myr-5V1-2 into the ventral tegmental area (VTA) or medial prefrontal cortex (mPFC), regions that are known to mediate the reinforcing effects of ethanol. In Specific Aim 3, we will examine the neural circuitry whereby mGluR5-PKC5 signaling mediates cue-induced reinstatement of ethanol-seeking behavior. This will be examined by measuring cue-evoked ethanol-seeking following microinjection of the selective mGluR5 antagonist MTEP alone and in combination with the PKC5 translocation inhibitor myr-5V1-2 into the VTA or basolateral amygdala (BLA), regions that are known to mediate stimulus- reward associations. Together, the proposed studies will provide insight into the bidirectional crosstalk between mGluR5 and PKC5 and the role this signaling pathway plays in ethanol self-administration and cue-evoked relapse-like behavior, which will hopefully lead to improved treatments for alcoholism and other alcohol use disorders. PUBLIC HEALTH RELEVANCE: The goal of this proposal is to investigate the role of mGluR5-PKC5 signaling in the regulation of ethanol consumption and relapse in rodents. Further understanding of the contributions of mGluR5 and PKC5 signaling to these behaviors will hopefully translate into improved therapies for the treatment of alcoholism in humans.